1. Field of the Invention
The present invention relates to a motor driving control method and a motor driving control device in each of which current flows through the coil of a motor to thereby drive the motor.
2. Description of the Related Art
A driving control method of a single-phase motor will be explained below.
A description of a configuration of a motor driving control device 101 of a comparative example will be provided with reference to FIG. 10.
The motor driving control device 101 controls the driving of a motor 20 as a single-phase brushless motor. The motor 20 includes a position detector 30 as a Hall element, for example, and a motor coil Lm. The motor driving control device 101 includes a control circuit 104, a pre-drive circuit 103 and an H-bridge circuit 102.
The control circuit 104 generates a drive control signal Sd based on a position detection signal (positional information) Sp from the position detector 30 and outputs the drive control signal Sd to the pre-drive circuit 103.
The pre-drive circuit 103 generates drive signals H1, H2, L1 and L2 based on the drive control signal Sd. The drive signals H1, H2, L1 and L2 thus generated are output to the H-bridge circuit 102.
The H-bridge circuit 102 includes a first series circuit having first and second switching elements Q1, Q2 connected between a DC power source Vdd and the ground, and a second series circuit having a third and fourth switching elements Q3, Q4 connected in parallel to the first series circuit.
Each of the first and third switching elements Q1 and Q3 is a P-type MOSFET (metal-oxide-semiconductor field-effect transistor). Each of the second and fourth switching elements Q2 and Q4 is an N-type MOSFET. The motor coil Lm of the motor 20 is connected between a connection node of the first switching element Q1 and the second switching element Q2 and a connection node of the third switching element Q3 and the fourth switching element Q4.
The motor driving control device 101 turns on/off the first and fourth switching elements Q1, Q4 and the second and third switching elements Q2, Q3 in a complementary manner to thereby change the direction of a coil current IL flowing through the motor coil Lm. The motor is driven in this manner. A comparative example of the operation of the switching elements during respective energization control periods is shown FIG. 11.
In this case, as a concrete example, the operation states of the first and fourth switching elements Q1 to Q4 according to the energization control of the motor driving control device 101.
During a first energization control period (first period), the first switching element Q1 is subjected to PWM (Pulse Width Modulation) control. Each of the second and third switching elements Q2, Q3 is turned off. The fourth switching element Q4 is turned on. Incidentally, the first switching element Q1 may not be subjected to PWM control but may be controlled so as to be in an on state.
During a PWM control period (second period), the first switching element Q1 is subjected to PWM control with a predetermined on-duty. In this case, a PWM pulse of one period is output based on turning-on and turning-off of this switching element. Each of the second and third switching elements Q2, Q3 is turned off like the first energization control period. The fourth switching element Q4 is turned on like the first energization control period.
During an all-phase off control period (third period), each of the first and fourth switching elements Q1 to Q4 is turned off.
During a second energization control period (fourth period), the third switching element Q3 is subjected to PWM control. The second switching element Q2 is turned on. Each of the first and fourth switching elements Q1, Q4 is turned off. Incidentally, the third switching element Q3 may not be subjected to PWM control but may be controlled so as to be in an on-state.
An example of the change of the coil current in the comparative example is shown in FIG. 12. The change of the coil current IL flowing through the motor coil in the control method is described with a graph, having an vertical axis that represents a current value and an horizontal axis that represents the time.
During the first energization control period, the coil current maintains a current value.
As time progresses during the PWM control period from a first time point t11 to a second time point t12, the coil current IL current value Ib of the second time point is reduced compared to that from the current value Ia of the previous first time point.
During the all-phase off control period from the second time point t12 to a third time point t13, the coil current IL reduces abruptly and becomes 0 A.
During the second energization control period on and after the third time point t13, the coil current IL gradually reduces and reaches a negative current value (−Ia) and thereafter maintains this negative current value (−Ia).
In this manner, according to the control method of the comparative example, since the all-phase off control period is provided at the time of switching the energization, the direction of flow of the coil current IL flowing through the motor coil Lm changes abruptly while accumulating a lot of energy in the motor coil Lm. Thus, a large regenerative current flows through a power source line and hence a serious inductive kickback occurs. As a result, a problem arises wherein the vibration of the single-phase motor and noise become large.
In view of such a problem, there is disclosed a motor control method for suppressing the inductive kickback. JP-A-2009-296850 describes a method for controlling a motor by controlling a motor coil bridged between a first transistor to a fourth transistor includes: a first energization control step of flowing current from the first transistor to the fourth transistor side through the motor coil; a first PWM control step of performing PWM control on the first transistor; a regenerative control step of generating regenerative current so as to flow from the third transistor to the fourth transistor side through the motor coil; a non-overlap control step of flowing current from the third transistor to the fourth transistor side though the motor coil; a second
PWM control step of executing PWM control on the second transistor; and a second energization control step of stopping the PWM control on the second transistor and flowing current from the second transistor to the third transistor side through the motor coil.
The motor control method described in JP-A-2009-296850 has the following problem. That is, in a case that an amount of energy to be regenerated is relatively small, energy accumulated in the motor coil can be entirely released by the regenerative control step and the non-overlap control step etc. However, in a case that an amount of energy to be regenerated is relatively large, energy accumulated in the motor coil can not be effectively released even by using these control steps. Thus, the motor may vibrate and noise may be generated due to the inductive kickback.